Applied. Microbiol. Biotechnol., 1994, Vol. 41, pp. 99-105 and Journal of fermentation and Bioengineering, 1997, Vol. 84, pp. 337-341 have disclosed stimuli-responsible magnetic fine particles wherein polyisopropylacrylamide having a lower critical solution temperature (hereinafter referred to as “LCST”) are immobilized to magnetic fine particles having a particle size of about 100 to 200 nm.
Since the stimuli-responsible magnetic fine particles have a small particle size of about 100 to 200 nm, the particles can be well dispersed in water. When an aqueous solution of the stimuli-responsible magnetic fine particles is heated to raise the temperature to the LCST or higher, the stimuli-responsible magnetic fine particles precipitate and aggregate. Since the aggregate can be easily recovered by magnetism, there are attempts to separate a variety of biological molecules and microorganisms using the stimuli-responsible magnetic fine particles to which an antibody or antigen is immobilized.
However, in the case of separating a biological molecule or the like by the above-mentioned method, it is necessary to raise the temperature of a solution containing the objective substance and the stimuli-responsible magnetic fine particles. Depending on the LCST of the stimuli-responsible magnetic fine particles to be used and also thermal stability of the objective substance, the biological substance or the like as the objective substance may be damaged or inactivated in some cases.